1. Field of the Invention
The present invention relates to a ceramic porous material having a bubble-like appearance to be used as a filter, a bubbler, a gas supplying member, a semiconductor producing device member, an artificial bone, a cell culturing supporter, an artificial organ, a catalyst supporter, or the like, and a production method therefor.
2. Description of the Related Art
Conventionally, as a ceramic porous material of this kind, one having a three-dimensional mesh-like skeleton structure with a large number of substantially spherical adjacent cells (pores) communicating with each other via communication holes has been known (see the official gazette of the Japanese Patent Laid Open Application (JP-A) No. 4-202071 (U.S. Pat. No. 2,506,502).
The ceramic porous material is produced by preparing a slurry by dispersing or dissolving in a solvent a ceramic powder and an organic substance to be hardened by the cross-linking polymerization, adding a cross-linking agent to the slurry, molding and hardening (gellation molding) in an agitated and bubbled state, drying the compact and baking (fireing, sintering).
However, according to the conventional ceramic porous material, problems are involved in that the mechanical strength is low, dusts (particles) are generated, and the transmissivity is poor.
In order to find the cause of the problems, the periphery of the communication holes in the skeleton structure was observed with a scanning type electron microscope so that an abnormal form of crystal particles forming the rim of the communication holes was observed.
That is, at the rim of the communication holes, single particles of a cockscomb shape and a cactus shape were observed. Moreover, the fact that minute holes of the size equivalent to the crystal particle size, communicating the adjacent pores were found at the rim part of the communication holes and the growth of the crystal particles are restrained at the rim of the communication holes was found.
It can easily be assumed that the above-mentioned crystal particle growth abnormal part became the breakage starting point when the external force was applied to the ceramic porous material so as to cause stress concentration, and furthermore, the cockscomb shaped and cactus shaped parts were peeled off so as to generate dusts.
Accordingly, it is considered that the abnormal form of the crystal particle growth forming the rim of the communication holes is generated in the production process of the ceramic porous material.
That is, the cells of the slurry stage are formed by the liquid medium containing the ceramic powder, and in most cases by the aqueous slurry. The slurry before hardening is moved by the surface tension and parts between the adjacent cells are partially thinned and broken so as to form the communication holes. The communication hole rims linking the cells accordingly formed are of a sharp shape because they are broken after thinning and the viscosity of the slurry at the time of breaking is high and the flowability after film breakage to rounding the rims is low. Or in the case of forming the communication holes by breaking the thin film at the time of expansion and shrinkage of the air in the cells due to the temperature change after drying, or the like, the small pieces of the dried substances generated by the breakage can be adhered on the wall surface of the cells.
The average particle sizes of the crystal particles at the rim of the communication holes of the alumina ceramic porous material of the 80% porosity (baked at 1,600° C. for 2 hours in the air), at a position 2 μm away from the rim, and at a position 4 μm away from the rim were 0.80 μm, 1.67 μm, and 1.81 μm, respectively, and it was 8.52 μm at a position 100 μm away from the rim. The average particle sizes of the crystal particles at the rim of the communication holes of the hydroxyl apatite porous material of the 75% porosity (baked at 1,200° C. for 2 hours in the air), at a position 0.5 μm away from the rim, at a position 1 μm away from the rim, and at a position 1.5 μm away from the rim were 0.42 μm, 0.5 μm, and 0.55 μm, and 0.62 μm, respectively. Moreover, the average particle sizes of the crystal particles at the rim of the communication holes of the silicon carbide porous material of the 75% porosity (baked at 2300° C. for 2 hours in the reduced pressure argon gas atmosphere), at a position 2 μm away from the rim, and at a position 4 μm away from the rim were 0.49 μm, 4.38 μm, and 4.38 μm, respectively.